whichever used car you purchase will most likely require some form of maintenance/repairs to get it back running properly. Thats why its always advisable to get a reputable person to check the whole car and test drive it before purchasing it. It simply gives a good idea on how much you will need to spend after the purchase to get it running as per your liking.
Many FC and FD out there have been through some thrashing, lets face it, its a sports car so obviously ure gona 'tekan' da bugger. Point is to mod it properly to suit ure driving style and purpose of the car like weekend drive, track racing, daily drive etc.
From my experience and limited knowledge of the RE's Id say maintaining the FC is cheaper then the RX8 but dont take my word whole. U can ask the current FC drivers in here and they can share their experiences. Occasionally replacing some parts can be expensive as they maybe new and you cant get used but the part replaced should last you a great deal of time before requires replacing again.
If you purchase Bhowlings car, you can opt to remove the cage and replace the bumper to a model that you like. Its the same case for any other car too